Feed-forward of multi-layer and multi-process information using xps and xrf technologies

ABSTRACT

Methods and systems for feed-forward of multi-layer and multi-process information using XPS and XRF technologies are disclosed. In an example, a method of thin film characterization includes measuring first XPS and XRF intensity signals for a sample having a first layer above a substrate. The first XPS and XRF intensity signals include information for the first layer and for the substrate. The method also involves determining a thickness of the first layer based on the first XPS and XRF intensity signals. The method also involves combining the information for the first layer and for the substrate to estimate an effective substrate. The method also involves measuring second XPS and XRF intensity signals for a sample having a second layer above the first layer above the substrate. The second XPS and XRF intensity signals include information for the second layer, for the first layer and for the substrate. The method also involves determining a thickness of the second layer based on the second XPS and XRF intensity signals, the thickness accounting for the effective substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/140,340, filed on Sep. 24, 2018, which is a continuation of U.S.patent application Ser. No. 15/322,093, filed on Dec. 23, 2016 (now U.S.Pat. No. 10,082,390), which is a U.S. National Phase application under35 U.S.C. § 371 of International Application No. PCT/US2015/036619,filed on Jun. 19, 2015, which claims the benefit of U.S. ProvisionalApplication No. 62/016,211, filed on Jun. 24, 2014, the entire contentsof which are hereby incorporated by reference herein.

BACKGROUND 1) Field

Embodiments of the invention are in the field of semiconductor metrologyand, in particular, methods and systems for feed-forward of multi-layerand multi-process information using X-ray photoelectron spectroscopy(XPS) analysis and X-ray fluorescence (XRF) analysis technologies.

2) Description of Related Art

X-ray photoelectron spectroscopy (XPS) is a quantitative spectroscopictechnique that measures the elemental composition, empirical formula,chemical state and electronic state of the elements that exist within amaterial. XPS spectra may be obtained by irradiating a material with abeam of X-rays while simultaneously measuring the kinetic energy andnumber of electrons that escape from the top, e.g., 1 to 10 nm of thematerial being analyzed. XPS analysis commonly employs monochromaticaluminum Kα (AlKα) X-rays, which may be generated by bombarding analuminum anode surface with a focused electron beam. A fraction of thegenerated AlKα X-rays is then intercepted by a focusing monochromatorand a narrow X-ray energy band is focused onto the analysis site on asample surface. The X-ray flux of the AlKα X-rays at the sample surfacedepends on the electron beam current, the thickness and integrity of thealuminum anode surface, and crystal quality, size, and stability of themonochromator.

X-ray fluorescence (XRF) is the emission of characteristic “secondary”(or fluorescent) X-rays from a material that has been excited bybombarding with higher energy X-rays or gamma rays. The phenomenon iswidely used for elemental analysis and chemical analysis, particularlyin the investigation of metals, glass, ceramics and building materials,and for research in geochemistry, forensic science and archaeology.

XPS analysis and XRF analysis each have their own advantages. However,advances are needed in analyses based on XPS and/or XRF detection.

SUMMARY

One or more embodiments are directed to methods and systems forfeed-forward of multi-layer and multi-process information using XPS andXRF technologies.

In an embodiment, a method of thin film characterization includesmeasuring first XPS and XRF intensity signals for a sample having afirst layer above a substrate. The first XPS and XRF intensity signalsinclude information for the first layer and for the substrate. Themethod also involves determining a thickness of the first layer based onthe first XPS and XRF intensity signals. The method also involvescombining the information for the first layer and for the substrate toestimate an effective substrate. The method also involves measuringsecond XPS and XRF intensity signals for a sample having a second layerabove the first layer above the substrate. The second XPS and XRFintensity signals include information for the second layer, for thefirst layer and for the substrate. The method also involves determininga thickness of the second layer based on the second XPS and XRFintensity signals, the thickness accounting for the effective substrate.

In another embodiment, a system for characterizing a thin film includesan X-ray source for generating an X-ray beam. The system also includes asample holder for positioning a sample in a pathway of said X-ray beam.The system also includes a first detector for collecting an X-rayphotoelectron spectroscopy (XPS) signal generated by bombarding saidsample with said X-ray beam. The system also includes a second detectorfor collecting an X-ray fluorescence (XRF) signal generated bybombarding said sample with said X-ray beam. The system also includes acomputing device configured to determine a thickness of a second layerof the sample based on the XPS and XRF signals. The determining thethickness accounts for an estimated effective substrate based on a firstlayer and a substrate of the sample, the first layer and substrate belowthe second layer of the sample.

In another embodiment, a non-transitory machine-accessible storagemedium having instructions stored thereon which cause a data processingsystem to perform a method of method of thin film characterization. Themethod includes measuring first XPS and XRF intensity signals for asample having a first layer above a substrate. The first XPS and XRFintensity signals include information for the first layer and for thesubstrate. The method also involves determining a thickness of the firstlayer based on the first XPS and XRF intensity signals. The method alsoinvolves combining the information for the first layer and for thesubstrate to estimate an effective substrate. The method also involvesmeasuring second XPS and XRF intensity signals for a sample having asecond layer above the first layer above the substrate. The second XPSand XRF intensity signals include information for the second layer, forthe first layer and for the substrate. The method also involvesdetermining a thickness of the second layer based on the second XPS andXRF intensity signals, the thickness accounting for the effectivesubstrate.

In an embodiment, a method of thin film characterization includesmeasuring a first XPS intensity signal for a sample having a first layerabove a substrate. The first XPS intensity signal includes informationfor the first layer and for the substrate. The method also involvesdetermining a thickness of the first layer based on the first XPSintensity signal. The method also involves combining the information forthe first layer and for the substrate to estimate an effectivesubstrate. The method also involves measuring a second XPS intensitysignal for a sample having a second layer above the first layer abovethe substrate. The second XPS intensity signal includes information forthe second layer, for the first layer and for the substrate. The methodalso involves determining a thickness of the second layer based on thesecond XPS intensity signal, the thickness accounting for the effectivesubstrate.

In an embodiment, a method of thin film characterization includesmeasuring a first XRF intensity signal for a sample having a first layerabove a substrate. The first XRF intensity signal includes informationfor the first layer and for the substrate. The method also involvesdetermining a thickness of the first layer based on the first XRFintensity signal. The method also involves combining the information forthe first layer and for the substrate to estimate an effectivesubstrate. The method also involves measuring a second XRF intensitysignal for a sample having a second layer above the first layer abovethe substrate. The second XRF intensity signal includes information forthe second layer, for the first layer and for the substrate. The methodalso involves determining a thickness of the second layer based on thesecond XRF intensity signal, the thickness accounting for the effectivesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic schematic example that illustrates the XPS+XRFcombined technology measurement choreography of XPS and/or XRFfeed-forward, in accordance with an embodiment of the present invention.

FIG. 2 is a plot corresponding to a first operation in a feed-forwardprocess, in accordance with an embodiment of the present invention.

FIG. 3 is a plot corresponding to a second operation in the feed-forwardprocess, in accordance with an embodiment of the present invention.

FIG. 4 is a plot corresponding to a third operation in the feed-forwardprocess, in accordance with an embodiment of the present invention.

FIG. 5 illustrates a three-operation ZAZ application involvingZrO₂→Al₂O₃/ZrO₂→ZrO₂/Al₂O₃/ZrO₂, in accordance with an embodiment of thepresent invention.

FIG. 6 illustrates a mixing model used to characterize the ZrO₂ film ofFIG. 5, in accordance with an embodiment of the present invention.

FIG. 7 is an illustration representing a film measurement system havingXPS and XRF detection capability, in accordance with an embodiment ofthe present invention.

FIG. 8 is an illustration representing another film measurement systemhaving XPS and XRF detection capability, in accordance with anembodiment of the present invention.

FIG. 9 is an illustration representing a film measurement system havingXPS detection capability, in accordance with an embodiment of thepresent invention.

FIG. 10 illustrates a block diagram of an exemplary computer system, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Methods and systems for feed-forward of multi-layer and multi-processinformation using XPS and XRF technologies are described. In thefollowing description, numerous specific details are set forth, such asapproximation techniques and system arrangements, in order to provide athorough understanding of embodiments of the present invention. It willbe apparent to one skilled in the art that embodiments of the presentinvention may be practiced without these specific details. In otherinstances, well-known features such as entire semiconductor devicestacks are not described in detail in order to not unnecessarily obscureembodiments of the present invention. Furthermore, it is to beunderstood that the various embodiments shown in the Figures areillustrative representations and are not necessarily drawn to scale.

To provide context, various electronic events may occur when a sampleincluding a layer disposed above a substrate is bombarded with X-rays.For example, an electron may be released from the sample. X-rayphotoemission may occur for an electron generated within the top, e.g.,10 nanometers of the sample. Most information from an XPS measurement isusually obtained near the surface since attenuation of the electronsignal occurs as the electrons travel through material on their way out.For measurements deeper in the sample (e.g., 0.1-2 microns deep), X-rayfluorescence (XRF) may be used since XRF signals typically attenuate1000 times less than XPS photoelectron signals and are thus lesssusceptible to effects of depth within a sample.

One or more embodiments described herein are directed to (1) thedetection and use of photo-electron (XPS) and X-ray fluorescent (XRF)signals from single and multi-layer films to determine thickness andcomposition, along with (2) specification and algorithmic determinationof feed-forward film information from a “pre” measurement operation to“post” process measurements in order to determine the most accurate andstable process control of thickness and composition. In someembodiments, the results from intermediate XPS/XRF process measurementsare saved in a database that is simultaneously accessible to allmeasurement tools, enabling a feed-forward solution across a fleet ofsystems. More generally, embodiments are directed to measuring XPS andXRF signals, combining signals in a global, simultaneous fit using afilm stack that properly accounts for the predicted XPS and XRFintensities at subsequent operations by direct or model-based methods.

To provide further context, one or more embodiments described herein maybe implemented to address issues otherwise associated with simultaneousdetermination and process control of complex, multi-layer films havingthickness and compositional material (atomic composition or AC %) thatrequire stringent process control. By contrast, state-of-the-artapproaches involve resolving such issues by spectroscopic ellipsometryand reflectometry or other traditional methods in an attempt tosimultaneously determine the thickness and composition using amulti-operation feed forward methodology.

In accordance with an embodiment of the present invention, technicaladvantages of approaches described herein involve the use of XPS and XRFmeasurements while allowing for the use of fundamental measurementinformation from a pre measurement to be usefully employed in subsequentfilm models for post measurements. In one embodiment, such an approachprovides a highly decoupled problem at each operation, which is unlikeother technologies where the complexity of the previous films andresults must be carried forward at each subsequent operation.

Implementation of certain embodiments described herein involves thecombination of XPS and XRF signals along with realistic film stackmodels to simultaneously determine the thickness and compositional filmproperties in a multi-operation thickness and composition near thesample surface, the ability to feed-forward results from previousprocess/metrology operations into an increasingly thicker, more complexfilm stack fundamentally extends the capability of XPS (and incombination with XRF) for fab process control.

In more specific embodiments, since XPS and XRF are both intensity-basedtechnologies, it is possible to effectively de-couple multi-operationmeasurements in a very clean and fundamental way by feeding forward preresults to the subsequent film substrate model information thatspecifies the relative intensity of the underlying species for postmeasurements. The effective substrate model at each operation containsthe relevant species from the previous operation, and an intensityproduction factor that scales with the bulk AC % value from the previousmeasurement.

It is to be appreciated that XPS+XRF feed-forward approaches describedherein may be implemented in several different ways. In an embodiment,the information fed forward can be model-independent, only depending onthe fundamental atomic sensitivity factors (ASF's). In this case,intensity-only determined “bulk AC %” values at each operation areforwarded into an effective substrate model at the subsequent operationfor the most accurate thickness and composition determination. Inanother embodiment, feeding forward thickness-only information may besufficient, or a calculated effective substrate result may be used, andshould be considered a complimentary approach contained within a broaderscope of embodiments described herein. In any of the approachesdescribed herein, in an embodiment, in order to enable the fullfeed-forward solution across single- and multiple systems in a fabenvironment, a database is required for real-time storing and retrievalof pre results.

As a representative example, FIG. 1 is a basic schematic example thatillustrates the XPS+XRF combined technology measurement choreography ofXPS and/or XRF feed-forward, in accordance with an embodiment of thepresent invention. Referring to FIG. 1, a first layer 102 is formedabove a substrate 100. The first layer 102 includes species B and C,while the substrate 100 includes species A. For the pre-measurementoperation, intensities from species A, B and C are measured, andcomposition and/or thickness is determined and stored in a database. Asecond layer 104 is then formed above the first layer 102. In oneembodiment, the second layer 104 includes species A along with a newspecies D.

In an embodiment, for the post-measurement where the second layer 104 isdeposited, the accurate determination of composition and/or thickness ofthe second layer 104 requires specification of only the effectiveintensity contribution of the original A,B,C signals from thepre-measurement. Thus, the first layer 102 and the substrate 100 areeffectively treated as a single incoming layer or substrate 100′(“effective substrate). This can be enabled by direct AC % fromintensities only, and/or model-derived results.

Referring again to FIG. 1, then, pre-measurement involves determinationof first layer 102 thickness and composition. The relative intensitiesof species A, B and C are calculated. A feed forward of the informationof the so-called previous layer with results for all relativeintensities is then used in a post-measurement. The post-measurementinvolves a determination of the thickness and composition (e.g., speciesA and new species D) of the second layer 104. The determination accountsfor the effective substrate 100′.

A first specific example of a multi-operation/multi-process film resultusing feed forward of XPS results is described below in association withFIGS. 2, 3 and 4. The example involves a titanium nitride (TiN)/high-kdielectric (HiK) sample.

FIG. 2 is a plot 200 corresponding to a first operation in afeed-forward process, in accordance with an embodiment of the presentinvention. Referring to plot 200, measured titanium nitride (TiN)thickness in Angstroms (A) is plotted as a function of nominal targetTiN thickness. It is to be appreciated that the measurement may be TiNonly or may be TiN and HiK as a combination. In an embodiment, for thefirst measurement operation (plot 200), results for each wafer TiNthickness split are saved in a feed-forward database.

FIG. 3 is a plot 300 corresponding to a second operation in thefeed-forward process, in accordance with an embodiment of the presentinvention. Referring to plot 300, measured titanium aluminum carbide(TiAlC) thickness in Angstroms (A) is plotted as a function of TiAlCdeposition cycles, where the TiAlC is deposited above the TiN/HiK of thefirst operation. The TiN/Hik thickness results from the first operationare fed-forward site-by-site to the second process and measurementoperation (to generate plot 300). Thus, the second operation involvesdeposition and measurement of TiAlC, the measurement involving use ofthickness results from the first operation.

FIG. 4 is a plot 400 corresponding to a third operation in thefeed-forward process, in accordance with an embodiment of the presentinvention. Referring to plot 400, measured titanium nitride (TiN)thickness in Angstroms (A) is plotted as a function of target TiNthickness. The TiN is deposited above TiAlC of the second operation. Thetop TiN film thickness at this third operation is determined usingresults from previous two process operations. Thus, the third depositionand measurement operation is top TiN, using the thickness results fromthe first and second operations described above. The linearity of themeasured results with the expected result at each operation is clearlydemonstrated in plot 400.

As a second specific example of a multi-operation/multi-process filmresult using a feed forward approach, a three-operationZrO₂/Al₂O₃/ZrO₂/Substrate (ZAZ/Substrate) application is described belowin association with FIGS. 5 and 6.

FIG. 5 illustrates a three-operation ZAZ application involvingZrO₂→Al₂O₃/ZrO₂→ZrO₂/Al₂O₃/ZrO₂, in accordance with an embodiment of thepresent invention. Referring to FIG. 5, structure 500 includes a layerof zirconium oxide (ZrO₂) 504 on silicon nitride (SiN) layer 502. TheZrO₂ layer 504 is associated with a signal intensity for zirconium(I(Zr)) and an intensity signal for oxygen (I(O)). The SiN layer 502 isassociated with a signal intensity for silicon nitride (I(Si—N)). Whendetermining a thickness of the ZrO₂ layer 504, the underlying I(Si—N)intensity signal is attributed to the underlying SiN “substrate.”

For the next structure 510 of FIG. 5, an aluminum oxide (Al₂O₃) layer514 has been deposited on the structure 500. The Al₂O₃ layer 514 isassociated with a signal intensity for aluminum (I(Al)) and an intensitysignal for oxygen (I′(O)). When determining a thickness of the Al₂O₃layer 514, the underlying I(Si—N), I(Zr) and I(O) intensity signals areattributed to an underlying “effective substrate I” 512 that accountsfor intensity signals from the SiN 502 and the ZrO₂ layers 504 from thestructure 500.

For the next structure 520 of FIG. 5, a second zirconium oxide (ZrO₂)layer 524 has been deposited on the structure 510. The ZrO₂ layer 524 isassociated with a signal intensity for zirconium (I″(Zr)) and anintensity signal for oxygen (I′″(O)). When determining a thickness ofthe ZrO₂ layer 524, the underlying I′(Si—N), I′(Zr), I″(O) and I(Al)intensity signals are attributed to an underlying “effective substrateII” 522 that accounts for intensity signals from the SiN layer 502, thefirst ZrO₂ layer 504 and the Al₂O₃ layer 514.

FIG. 6 illustrates a mixing model used to characterize the ZrO₂ layer504 of FIG. 5, in accordance with an embodiment of the presentinvention. Referring to FIG. 6, the ZrO₂ layer 504 is modeled as amixing model 600, where the connection between the film AC % and mixingfraction is defined. In particular, the ZrO₂ layer 504 is modeled as a“pure Zr” film component 602 and a “pure O” film component 604. Thisprovides relative intensity signals for Zr (signal 610), O (signal 612)and the underlying SiN substrate 502 (signal 614). Referring again toFIG. 5, at the operation concerning structure 510, the intensityresponse of all prior species from the model 600 is encoded as aneffective substrate 512 with relative intensities calculated from thefirst operation (i.e., the operation illustrated in FIG. 6).

In another aspect of embodiments of the present invention, a filmmeasurement system includes both an XPS detector and an XRF detector.For example, FIG. 7 is an illustration representing a film measurementsystem having XPS and XRF detection capability, in accordance with anembodiment of the present invention.

Referring to FIG. 7, a film measurement system 700 includes an XPS/XRFgeneration and detection system housed in a chamber 701 coupled with acomputing system 722. The XPS/XRF generation and detection systemincludes an electron beam source 702 provided for generating an electronbeam 704. Electron beam 704 is used to generate an X-ray beam 708 bybombarding an anode 706. A monochromator 709 is provided fortransporting a monochromatized X-ray beam 710 from X-ray beam 708. Asample holder 711 may be used to position a sample 799 in a pathway ofmonochromatized X-ray beam 710.

An XPS detector 714 is provided for collecting an XPS signal 712generated by bombarding sample 799 with monochromatized X-ray beam 710.An XRF detector 716 is provided for collecting an XRF signal 718 alsogenerated by bombarding sample 799 with monochromatized X-ray beam 710.In an embodiment, system 700 is configured to collect XRF signal 718 andXPS signal 712 simultaneously or near simultaneously, representing asingle sampling event. The XPS signal 712 and XRF signal 718 arecomposed of photo-electrons and fluorescent X-rays, respectively.Additionally, a flux detector 720 may be provided for determining anestimated flux of monochromatized X-ray beam 710. In one suchembodiment, flux detector 720 is positioned at sample holder 711, asdepicted in FIG. 7. In another embodiment, an X-ray flux detector 721 isplaced near the monochromator to partially intersect a small fraction ofthe primary X-rays in order to monitor the X-ray flux while the sampleholder 711 is positioned at the analysis site, as is depicted in FIG. 7.

Computing system 722 includes a user interface 724 coupled with acomputing portion 726 having a memory portion 728. Computing system 722may be configured to calibrate an XPS signal detected by XPS detector714. Computing system 722 may be configured to calibrate the XRF signaldetected by XRF detector 716. Computing system 722 may be configured tomonitor the primary X-ray flux as measured by Flux detector 720 and/or721. In accordance with an embodiment of the present invention,computing system 722 is for normalizing an XPS signal detected by XPSdetector 714, as well as an XRF signal detected by XRF detector 716 withthe primary X-ray flux measured by Flux detector 720 or 721. In oneembodiment, memory portion 728 has stored thereon a set of instructionsfor, when executed, using monochromatized X-ray beam 710 to generate XPSsignal 712 and XRF signal 718 from sample 799.

FIG. 8 is an illustration representing another film measurement systemhaving XPS and XRF detection capability, wherein both XPS and XRFinformation may be obtained from a single metrology tool, in accordancewith an embodiment of the present invention. In FIG. 8, an angled viewof an XPS and XRF combination tool 800 is depicted. In one embodiment,the XPS and XRF combination tool 100 is capable of measuring 300 mmwafers within a 50 μm² metrology box.

Referring to FIG. 8, the XPS and XRF combination tool 800 is operatedwhile maintained under a base pressure of less than approximately 1.0E-7Torr. Using a LaB₆ electron gun 802 at a nominal beam current ofapproximately 600 μA, x-rays 804 are generated from an aluminum anode806 at 1486.7 eV. Monochromatic AlKα x-rays 808 is then focused on to awafer 810 by a high quality quartz crystal monochromator 812. A magneticlens 814 under the wafer 810 generates a magnetic field near the wafer810 surface and focuses the photoelectrons 816 generated into an XPSspectrometer including XPS input optics 818, an XPS energy analyzer 820(e.g., a Spherical Capacitor Analyzer (SCA)), and an XPS detector 822.The XPS spectrometer electron optics 818 directs and shapes thephotoelectron beam 816 for best transmission into the XPS energyanalyzer 820. The XPS energy analyzer 820 operates at fixed voltagedifference between the spheres, and a pass energy of 141.2 eV istypically used.

Referring again to FIG. 1, simultaneously, the monochromatic AlKα x-rays808 excites low energy x-ray fluorescence (LE-XRF) 824 from the wafer810. The LE-XRF 824 is detected by using a Silicon Drift Detector (SDD)826 located near the analysis point, approximately 1 mm above the wafer810 surface. In one embodiment, the SDD detector 826 is cooled by dualPeltier coolers, and the operating temperature is maintained atapproximately −30° C. To filter out stray electrons and UV light, anultrathin aluminum window may be used at the SDD 826 entrance. SDD 826is coupled to an XRF detector assembly 828. The XRF detector assembly828 is coupled to SDD electronics 830.

The XPS and XRF combination tool 800 may also include apost-monochromator flux detector 899, as is depicted in FIG. 8. Althoughnot depicted, XPS and XRF combination tool 800 may also be equipped withvision cameras. For example, a wafer-XY camera can be included forfeature finding and pattern recognition on the wafer. A wafer-Z cameracan be included for determining the wafer z-height for optimal x-rayspot focusing and positioning. An anode camera can be included thatmonitors the anode for optimal e-beam focus and position. Dataacquisition may be integrated to the system software where both XPS andXRF signals are collected at the same time. In one such embodiment,total acquisition time is approximately 24 s per site.

Although several of the above described embodiments involve feed-forwardtechniques for a combination of XPS and XRF measurements, it is to beappreciated that such techniques are also applicable for XRFmeasurements on their own, or for XPS measurements on their own.Accordingly, a suitable measurement apparatus may not be equipped withboth XRF and XPS measurement capabilities, but may be equipped with onlyone of XRF or XPS measurement capabilities. As an example, FIG. 9 is anillustration representing a film measurement system having only XPSdetection capability, in accordance with an embodiment of the presentinvention. As another example, although not depicted, a film measurementsystem has only XRF detection capability.

Referring to FIG. 9, a film measurement system 900 includes an XPSgeneration and detection system housed in a chamber 901 coupled with acomputing system 918. Computing system 918 includes a user interface 920coupled with a computing portion 922 having a memory portion 924. TheXPS generation and detection system includes an electron beam source 902provided for generating an electron beam 904. Electron beam 904 is usedto generate an X-ray beam 908 by bombarding an anode 906. Amonochromator 909 is provided for focusing a monochromatized X-ray beam910 from X-ray beam 908. A sample holder 911 may be used to position asample 999 in a pathway of monochromatized X-ray beam 910.

An XPS detector 914 is provided for collecting an XPS signal 912generated by bombarding sample 999 with monochromatized X-ray beam 910.Additionally, a flux detector 916 may be provided for determining anestimated flux of monochromatized X-ray beam 910. In one suchembodiment, flux detector 916 is positioned at sample holder 911, asdepicted in FIG. 9. In another embodiment, an X-ray flux detector 921 isplaced near the monochromator to partially intersect a small fraction ofthe primary X-rays in order to monitor the X-ray flux while the sampleholder 911 is positioned at the analysis site.

In an embodiment, whether a system is equipped with XPS detectioncapability only or both XPS and XRF detection capability, a method ofthin film characterization includes measuring a first XPS intensitysignal for a sample having a first layer above a substrate. The firstXPS intensity signal includes information for the first layer and forthe substrate. The method also involves determining a thickness of thefirst layer based on the first XPS intensity signal. The method alsoinvolves combining the information for the first layer and for thesubstrate to estimate an effective substrate. The method also involvesmeasuring a second XPS intensity signal for a sample having a secondlayer above the first layer above the substrate. The second XPSintensity signal includes information for the second layer, for thefirst layer and for the substrate. The method also involves determininga thickness of the second layer based on the second XPS intensitysignal, the thickness accounting for the effective substrate.

In another embodiment, whether a system is equipped with XRF detectioncapability only or both XPS and XRF detection capability, a method ofthin film characterization includes measuring a first XRF intensitysignal for a sample having a first layer above a substrate. The firstXRF intensity signal includes information for the first layer and forthe substrate. The method also involves determining a thickness of thefirst layer based on the first XRF intensity signal. The method alsoinvolves combining the information for the first layer and for thesubstrate to estimate an effective substrate. The method also involvesmeasuring a second XRF intensity signal for a sample having a secondlayer above the first layer above the substrate. The second XRFintensity signal includes information for the second layer, for thefirst layer and for the substrate. The method also involves determininga thickness of the second layer based on the second XRF intensitysignal, the thickness accounting for the effective substrate.

Embodiments of the present invention may be provided as a computerprogram product, or software, that may include a machine-readable mediumhaving stored thereon instructions, which may be used to program acomputer system (or other electronic devices) to perform a processaccording to the present invention. A machine-readable medium includesany mechanism for storing or transmitting information in a form readableby a machine (e.g., a computer). For example, a machine-readable (e.g.,computer-readable) medium includes a machine (e.g., a computer) readablestorage medium (e.g., read only memory (“ROM”), random access memory(“RAM”), magnetic disk storage media, optical storage media, flashmemory devices, etc.), a machine (e.g., computer) readable transmissionmedium (electrical, optical, acoustical or other form of propagatedsignals (e.g., infrared signals, digital signals, etc.)), etc.

FIG. 10 illustrates a diagrammatic representation of a machine in theexemplary form of a computer system 1000 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed herein, may be executed. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a Local Area Network (LAN), an intranet, an extranet, or theInternet. The machine may operate in the capacity of a server or aclient machine in a client-server network environment, or as a peermachine in a peer-to-peer (or distributed) network environment. Themachine may be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, switch or bridge, or any machinecapable of executing a set of instructions (sequential or otherwise)that specify actions to be taken by that machine. Further, while only asingle machine is illustrated, the term “machine” shall also be taken toinclude any collection of machines (e.g., computers) that individuallyor jointly execute a set (or multiple sets) of instructions to performany one or more of the methodologies discussed herein.

The exemplary computer system 1000 includes a processor 1002, a mainmemory 1004 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM(RDRAM), etc.), a static memory 1006 (e.g., flash memory, static randomaccess memory (SRAM), etc.), and a secondary memory 1018 (e.g., a datastorage device), which communicate with each other via a bus 1030.

Processor 1002 represents one or more general-purpose processing devicessuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processor 1002 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processor 1002 may alsobe one or more special-purpose processing devices such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), a digital signal processor (DSP), network processor, or thelike. Processor 1002 is configured to execute the processing logic 1026for performing the operations discussed herein.

The computer system 1000 may further include a network interface device1008. The computer system 1000 also may include a video display unit1010 (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)),an alphanumeric input device 1012 (e.g., a keyboard), a cursor controldevice 1014 (e.g., a mouse), and a signal generation device 1016 (e.g.,a speaker).

The secondary memory 1018 may include a machine-accessible storagemedium (or more specifically a computer-readable storage medium) 1031 onwhich is stored one or more sets of instructions (e.g., software 1022)embodying any one or more of the methodologies or functions describedherein. The software 1022 may also reside, completely or at leastpartially, within the main memory 1004 and/or within the processor 1002during execution thereof by the computer system 1000, the main memory1004 and the processor 1002 also constituting machine-readable storagemedia. The software 1022 may further be transmitted or received over anetwork 1020 via the network interface device 1008.

While the machine-accessible storage medium 1031 is shown in anexemplary embodiment to be a single medium, the term “machine-readablestorage medium” should be taken to include a single medium or multiplemedia (e.g., a centralized or distributed database, and/or associatedcaches and servers) that store the one or more sets of instructions. Theterm “machine-readable storage medium” shall also be taken to includeany medium that is capable of storing or encoding a set of instructionsfor execution by the machine and that cause the machine to perform anyone or more of the methodologies of the present invention. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, and optical and magneticmedia.

In an embodiment, a non-transitory machine-accessible storage mediumhaving instructions stored thereon which cause a data processing systemto perform a method of method of thin film characterization. The methodincludes measuring first XPS and XRF intensity signals for a samplehaving a first layer above a substrate. The first XPS and XRF intensitysignals include information for the first layer and for the substrate.The method also involves determining a thickness of the first layerbased on the first XPS and XRF intensity signals. The method alsoinvolves combining the information for the first layer and for thesubstrate to estimate an effective substrate. The method also involvesmeasuring second XPS and XRF intensity signals for a sample having asecond layer above the first layer above the substrate. The second XPSand XRF intensity signals include information for the second layer, forthe first layer and for the substrate. The method also involvesdetermining a thickness of the second layer based on the second XPS andXRF intensity signals, the thickness accounting for the effectivesubstrate.

Thus, methods and systems for feed-forward of multi-layer andmulti-process information using XPS and XRF technologies have beendescribed.

What is claimed is:
 1. A method for thin film characterization of asample, comprising: measuring first XPS and/or XRF intensity signals fora reference sample having a first layer above a substrate, the first XPSand/or XRF intensity signals including information for the first layerand for the substrate; determining at least one of a thickness or acomposition of the first layer based on the first XPS and/or XRFintensity signals; combining the information for the first layer and forthe substrate; measuring second XPS and/or XRF intensity signals for aninspected sample having a second layer above the first layer, the secondXPS and/or XRF intensity signals including information for the secondlayer, for the first layer and for the substrate; determining at leastone of a thickness or a composition of the second layer based on thesecond XPS and/or XRF intensity signals.
 2. The method of claim 1,wherein the data of the effective substrate comprises intensity data forrelevant atomic species of the substrate and the first layer.
 3. Themethod of claim 1, wherein combining the information for the first layerand for the substrate comprises generating an effective substrate data,and wherein the effective substrate data comprises bulk atomiccomposition values of the substrate and the first layer.
 4. The methodof claim 1, wherein combining the information for the first layer andfor the substrate comprises generating an effective substrate data, andwherein the effective substrate data comprises thickness onlyinformation of the substrate and the first layer.
 5. The method of claim1, wherein measuring XPS and/or XRF intensity signals for the samplecomprises simultaneously measuring XPS and XRF intensities.
 6. Themethod of claim 1, wherein combining the information for the first layerand for the substrate comprises combining signals in a global,simultaneous fit by direct or model-based methods to estimate aneffective substrate.
 7. The method of claim 1, further comprising usingan effective substrate model based on atomic species from the firstlayer and the substrate, and an intensity production factor that scaleswith a bulk atomic composition % value for the atomic species toestimate an effective substrate.
 8. The method of claim 1, whereincombining the information for the first layer and for the substratecomprises estimating an effective substrate, and wherein estimating theeffective substrate is a model-independent approach based on fundamentalatomic sensitivity factors (ASFs).
 9. The method of claim 1, whereincombining the information for the first layer and for the substratecomprises generating an effective substrate data, and wherein the methodcomprises determining both the thickness and the composition of thesecond layer based on the second XPS and/or XRF intensity signals andthe effective substrate data.
 10. The method of claim 9, whereinmeasuring XPS and/or XRF intensity signals for the sample comprisessimultaneously measuring XPS and XRF intensities.
 11. The method ofclaim 1, wherein combining the information for the first layer and forthe substrate comprises generating an effective substrate data, andfurther comprising: storing the effective substrate data; on anysubsequent measurement: fetching the effective substrate data from adatabase; determining a composition for the second layer of a subsequentmeasurement based on the second XPS and/or XRF intensity signals and theeffective substrate data.
 12. A method of thin film characterization ofa sample, the sample comprising a substrate, at least one intermediatelayer over the substrate, and a top layer over the intermediate layer,the method comprising: measuring XPS and/or XRF intensity signals forthe sample; fetching from a database an effective substrate model, theeffective substrate model comprising XPS and/or XRF pre-intensity datafrom a previous measurement of a sample having no top layer; determiningat least one of a thickness and a composition of the top layer based onthe XPS and/or XRF intensity signals for the sample and the effectivesubstrate model.
 13. The method of claim 12, wherein measuring XPSand/or XRF intensity signals for the sample comprises simultaneouslymeasuring XPS and XRF intensities.
 14. The method of claim 12, furthercomprising combining the XPS and XRF intensity signals and the effectivesubstrate model to determine both the thickness and the composition ofthe top layer.
 15. The method of claim 12, further comprising combininginformation of the top layer and the effective substrate model togenerate subsequent effective substrate model
 16. A system forcharacterizing a thin film, said system comprising: an X-ray source forgenerating an X-ray beam; a sample holder for positioning a sample in apathway of said X-ray beam; a first detector for collecting an X-rayphotoelectron spectroscopy (XPS) signal generated by bombarding saidsample with said X-ray beam; a second detector for collecting an X-rayfluorescence (XRF) signal generated by bombarding said sample with saidX-ray beam; and, a computing device configured to determine a thicknessor composition of a second layer of the sample based on the XPS and XRFsignals, wherein determining the thickness or composition accounts foran estimated effective substrate based on a first layer and a substrateof the sample, the first layer and substrate below the second layer ofthe sample.
 17. The system of claim 16, wherein the first detector andthe second detector are configured to collect the XPS signal and the XRFsignal from within an approximately 50 μm2 metrology box of the sample.18. The system of claim 16, further comprising: a post-monochromatorflux detector for normalizing the XRF signal with respect to an incomingx-ray flux for stable measurement.
 19. The system of claim 16, whereinthe X-ray beam is monochromatic AlKα x-ray beam.
 20. The system of claim16, further comprising: a quartz monochromator disposed along thepathway of the X-ray beam, between the X-ray source and the sampleholder.